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THE CONTRIBUTION OF LOW SURFACE BRIGHTNESS GALAXIES TO FAINT GALAXY COUNTS

机译：低表面亮度星系对模糊星系计数的贡献

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摘要

Recent observations have revealed a population of blue galaxies at intermediate redshift with a space density well in excess of expectations from the local luminosity function and standard cosmology. The colors and luminosities of these faint blue galaxies are similar to nearby low surface brightness (LSB) galaxies. Such galaxies are severely underrepresented in surveys used to define the local luminosity function, but could in principle be detected in deep surveys. If LSB galaxy density is high enough, the faint-galaxy counts could be explained without requiring rapid galaxy evolution. To explore the consequences of including LSB galaxies, we construct catalogs of simulated nonevolving galaxies drawn from a multivariate distribution of galaxy luminosities, central surface brightnesses, bulge/disk ratios, and spectral-energy distributions. We compare two models dominated by LSB galaxies to a "standard" nonevolving model. Model galaxies are convolved with seeing and selected in a manner that closely matches real surveys. For each model we compute the local B_J band luminosity function, H I mass function, number counts in the B_J I, and K bands, redshift distributions and color distributions. We find it possible to include a large population of LSB galaxies and incorporate a steep faint-end slope of the luminosity function in our simulations without violating the constraints on the local field-galaxy luminosity function or the H I mass function. For q_0 = 0.5, the most favorable model matches the counts to B = 23, but falls short of the observations at fainter magnitudes. The discrepancy at faint magnitudes is smaller in the I and K bands. The colors and redshift distributions remain roughly consistent with observations to B = 24. The most serious discrepancy with observations is in the distribution of r_e at faint magnitudes, suggesting that the model contains too many LSB galaxies. Nevertheless, the results suggest that LSB galaxies could be a significant contributor to faint-galaxy counts, reducing the need for such extreme models of galaxy evolution as rapid merging or bursting dwarf galaxies. We propose several tests to assess the contribution of LSB galaxies to faint galaxy counts and to differentiate models involving moderate galaxy evolution from models involving rapid merging or starbursts.
机译：最近的观察表明，处于中间红移状态的蓝色星系种群的空间密度远远超出了当地光度函数和标准宇宙学的预期。这些淡蓝色星系的颜色和亮度类似于附近的低表面亮度（LSB）星系。在用于定义局部光度函数的调查中，此类星系的代表性严重不足，但原则上可以在深度调查中检测到。如果LSB星系密度足够高，则可以解释微弱的星系计数而无需快速的星系演化。为了探索包括LSB星系的后果，我们从银河系亮度，中心表面亮度，凸出/圆盘比率和光谱能量分布的多元分布中构建了模拟无演化星系的目录。我们将以LSB星系为主的两种模型与“标准”无演化模型进行了比较。模型星系与可见物卷积在一起，并以与实际测量值非常匹配的方式进行选择。对于每个模型，我们计算局部B_J波段的亮度函数，H I质量函数，B_J I和K波段的数量计数，红移分布和颜色分布。我们发现有可能包括大量的LSB星系，并在我们的模拟中纳入光度函数的陡峭微弱斜率，而不会违反对局部场星系光度函数或H I质量函数的约束。对于q_0 = 0.5，最有利的模型将计数与B = 23匹配，但是在较弱的量级上缺少观测值。在I和K波段，幅度较小的差异较小。颜色和红移分布与B = 24的观测值大致保持一致。与观测值最严重的差异在于r_e在微弱数量级的分布，这表明该模型包含太多LSB星系。尽管如此，结果表明LSB星系可能是微弱星系计数的重要贡献者，从而减少了对诸如快速合并或爆发矮星系之类的极端星系演化模型的需求。我们提出了几种测试，以评估LSB星系对微弱星系计数的贡献，并将涉及中等星系演化的模型与涉及快速合并或爆炸的模型区分开。

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